Conventional articles of athletic footwear have included two primary elements, namely, an upper member and a sole member structure. The upper member provides at least a partial covering for the foot that securely receives and positions the foot with respect to the sole structure. In addition, the upper member may have structures and a configuration that protect the foot and provide ventilation, thereby cooling the foot and removing perspiration. The sole structure generally is secured to a lower portion of the upper member and generally is positioned between the foot and the ground. In addition to attenuating ground reaction forces (i.e., imparting cushioning), the sole structure may provide traction and help control foot motions, such as pronation. Accordingly, the upper member and the sole structure operate cooperatively to provide a comfortable structure that is suited for a variety of ambulatory activities, such as walking and running.
The sole member or structure of athletic footwear generally has exhibited a layered configuration that includes a comfort-enhancing insole, a resilient midsole (e.g., formed from a polymer foam material), and a ground-contacting outsole that provides both abrasion-resistance and traction. The midsole typically is the primary sole structure element that attenuates ground reaction forces and controls foot motions. Suitable polymer foam materials for the midsole include ethylvinylacetate or polyurethane that compress resiliently under an applied load to attenuate ground reaction forces. Conventional polymer foam materials are resiliently compressible, in part, due to the inclusion of a plurality of open or closed cells that define an inner volume substantially displaced by gas.
As noted above, various ground reaction force attenuating elements and systems have been known, including such elements and systems for use in footwear products including athletic footwear products. Conventionally, the structure, feel, and characteristics of such elements and systems are selected by a footwear manufacturer, and these elements and systems (as well as their associated characteristics) are permanently fixed in the footwear products once the footwear products are made. Each individual footwear user, however, possesses unique characteristics that affect their physical fitness or training regimes, such as weight, foot size, type of workout or exercise performed, stride or gait characteristics (e.g., a pronation or supination tendency), personal tastes and preferences, etc. Therefore, this “one size fits all” approach to footwear design and production can lead to uncomfortable fits and/or limited sales due to the failure of the footwear products to match the conditions or characteristics desired and/or preferred by users.
Accordingly, it would be useful to provide footwear products or other foot-receiving devices that are readily customizable to a user's tastes and specifications, e.g., based on the user's immediate needs and/or the characteristics he/she desires in the footwear product or other foot-receiving device in general and/or at a given time.